Larger helicopters, in general, have several features in common in a typical basic configuration or layout. For instance, a typical helicopter will have a cabin section rearward of the pilot's cockpit or flight deck and which is used to transport people, cargo or both. In addition, the helicopter will have an engine compartment which is located typically above and to the rear of the pilot's cockpit or flight deck, and above the cabin section. The engine compartment typically houses two primary components, at least one engine and a rotor transmission with a corresponding transmission housing.
Both the engine and the rotor transmission contain numerous fluids, such as petroleum-based lubricants, that are critical to the operation of the engine and the transmission. These fluids inevitably leak from various locations in the engine and the transmission during both the operation and storage of the helicopter. Because the engine compartment is generally oriented above the cabin section, any leaking fluids eventually seep or drip into the cabin section, unless proper sealing mechanisms are in place. The inflow of these leaking fluids spoil, stain or damage the cabin's interior materials such as seat covers and acoustic linings. In addition, the leaking fluids can severely damage or destroy sensitive electronic equipment that may be placed in the cabin section of a helicopter.
Moreover, the exterior of the helicopter around the engine and transmission compartment is not completely fluidtight, allowing fluid such as water to leak from these areas into the cabin with similar adverse effects.
During routine inspection and maintenance it is necessary to have both ready visual and physical access to portions of the engine or at least the rotor transmission. Such access is required to check critical fluid levels, to replace worn, damaged or depleted parts or filters, or to adjust mechanical systems. Typically, various access panels in or around the engine or transmission compartments provide the requisite openings to achieve ready access to the engine and the rotor transmission. In some helicopters, a forged or fixed airframe structure forms an access opening which is located below the rotor transmission housing and above the cabin section. The opening is thus accessible through the cabin's ceiling. This access opening, however, must be sealed by a cover against the inevitable oil and fluid drippings which the engine and the rotor transmission will produce, as well as against water leakage.
The access opening below the engine compartment in the prior helicopters, such as the BLACK HAWK® helicopter, made for the United States by Sikorsky Aircraft Company of Stratford, Conn., is defined by both the aircraft structural forgings and a flexible or yieldable downwardly-turned skirt which is riveted onto the helicopter's forged structure. The skirt is thin and many times more flexible relative to the helicopter's forged structure.
Prior drip pan designs attached a covering plate directly to the flexible skirt with a hollow seal sandwiched therebetween. One hollow seal used in prior designs resembled the flexible, hollow door seals used around car doors or refrigerator doors. However, the skirt contains surface aberrations, such as the protruding rivet heads from the rivets securing the skirt to the forged helicopter structure. When the seal engaged both the skirt and the rivet heads, it could be upset enough so that leakage occurred. Accordingly, the hollow seal traversing these aberrations while sandwiched between the skirt and the covering plate is unable to provide a suitable, consistent, long-term fluid seal. Moreover, flexing of the flexible skirt could also cause leakage.
Also, the geometry of the cover cannot be such that it protrudes significantly into the interior of the cabin section. Headroom in the cabin section typically is limited and any additional protrusion from the ceiling of the cabin section is undesirable. In addition, because weight is critical to the operation of any aircraft, heavy cover constructions are undesirable.
Other prior drip pan structures disclosed in U.S. Pat. Nos. 6,112,856; 6,216,823; 6,446,907 and Design U.S. Pat. No. D444,443, which are fully incorporated herein by this express reference, provided improvements and solutions to these difficulties. However, Sikorsky has now introduced its “M” Model BLACK HAWK® helicopter for which these prior structures are not readily adaptable due to a change in configuration of the skirt noted above.
In particular, while the prior drip pans provided a port for visual access to an oil filter, the port was offset from the filter, rendering it more difficult to see the filter from many viewing angles through the port, also requiring specially shaped tools to manipulate filter retention bolts and requiring tilting of filters when removed or replaced.
The “M” model is currently in the process of introduction by Sikorsky for use by U.S. Military. In that model, and in other aircraft with what are or will be similarly-shaped skirts, there is still a skirt as disclosed in the prior U.S. Pat. No. 6,446,907 with the exception that in the access area or corner for the filter, the corner of the skirt has been pulled outwardly to allow direct and straight-through access to the filter and its filter retention bolts where the pan is removed. Such direct access is preferable as it eliminates the need for the special dog-bone shaped tools necessary to operate the filter retention bolts to remove and install the filter as was required with the prior drip pan, which not only required such tools but also required the filter to be “tipped” as it was removed or replaced and before it could be seated (see FIG. 6 of U.S. Pat. No. 6,446,907). Accordingly, in the new “M” model, one corner of the old prior skirt has been pulled or extended outwardly and asymmetrically to the other corners.
Stated in another way, the radius point or center of the expanded corner curve of the skirt has been moved outwardly from its position in the prior drip pan and the straight sides of the skirt are no longer tangent to the curve of this corner.
Such modification of the skirt renders the prior symmetric frame and drip pan incompatible with the new “M” model air frame. There is or would be a gap between the new skirt at the expanded corner and the old drip pan and drip pan frame. Accordingly, there is no way for the old drip pan and frame structure of the prior patents, including U.S. Pat. No. 6,446,907, to provide sealing for the new “opened” corner defined by the new skirt to allow more direct access to the filter.
In order to overcome this problem, the old frame and drip pan could be re-shaped to the new skirt shape, however, the requirement to seal the pan peripherally to the frame in such a case would require extensive and expensive re-working of the peripheral seal structure of the pan. In particular, the pan would require a special seal seat groove to be milled or otherwise manufactured into the edge of the pan.
Specifically, since the straight skirt sides extend in a direction intersecting with, and are no longer tangent to, the skirt curve at this corner, the skirt takes on inwardly-facing convex shapes, directed inwardly of the access opening, before flowing into the new expanded inwardly-facing concave corner. This skirt configuration would require a cooperative configuration of the drip pan whose cover would follow that of the skirt. When a drip pan for a corresponding frame is so shaped, the peripheral o-ring sealing the drip pan to the frame cannot be used as with the prior o-ring groove due to the changed configuration of the sealing surfaces. When stretched to fit, the o-ring on the drip pan would not follow this curved portion of the pan because it would span across the corresponding outwardly-facing concave drip pan curves. Thus, the fit of the o-ring would render installation of the pan to the frame problematical and adversely affect the desired seal.
In other words, the spanning o-ring would interfere with the corresponding inwardly-facing convex curve of the frame when the pan was inserted therein. This would, in turn, require the provision of a much more expensive and complicated o-ring retaining groove in the peripheral edge of the removable pan.
Moreover, the aforesaid problem of visual access to the filter through the corresponding site port has remained a problem. It is desired to enhance the location of the port to facilitate more visual access to the filter and to its “bypass button” from more viewing locations. The retention of the prior site port in its same position relative to the old drip pan, however, would retain the visual disadvantages mentioned.
Accordingly, it is one objective to provide an improved leak-proof drip pan apparatus for use in “M” model BLACK HAWK® helicopters.
A further objective of this invention is to provide an improved cover and seal for the interior access opening of helicopters such as the BLACK HAWK® “M” model helicopter and those of similar structure.
Another object of this invention is to provide a drip pan that will effectively and consistently seal fluid from passage from an engine or transmission compartment to a cabin section of a BLACK HAWK® “M” model helicopter and similar air frames.
Another object of this invention is to provide a drip pan which permits quick visual and physical access to the engine or transmission compartment of a BLACK HAWK® “M” model helicopters and similar helicopters without requiring modification to the existing aircraft structure.
Another objective of the invention is to more effectively seal a drip pan to the skirt defining a transmission access opening in a BLACK HAWK® “M” model helicopters and similar helicopters.
Still another object of this invention is to provide a drip pan that can be attached to the existing structure of a BLACK HAWK® “M” model helicopter and similar helicopters without modification of the existing airframe structure and with minimal intrusion into the helicopter's cabin section.
Another objective of the invention is to provide an improved drip pan for use with BLACK HAWK® “M” model helicopter and similar air frames using an o-ring seal between drip pan and frame, where all peripheral curves in the pan are convex (i.e., outwardly directed) with respect to the pan.
Yet another objective of the invention is to provide enhanced visual access to a filter in an “M” model BLACK HAWK® helicopter.